The Soane museum is to have a very delicate makeover, says Richard Dorment.

The Oxford Dictionary of Architecture calls Sir John Soane’s Museum “one of the most complex, intricate, and ingenious series of interiors ever conceived”. It is also a delightful rabbit warren of a place, with interlocking rooms on different levels crammed from floor to ceiling with pictures, prints, drawings, plaster casts, antique fragments, books and architectural models.

The man who created it all was a discriminating collector with the hoarding mentality of a pack rat and a horror of an empty space. Sir John Soane displayed his collections with an eye for decorative pattern and symmetry, and not, as is usual in art galleries, to distinguish what is historically or aesthetically important from what is not.

True, masterpieces by Canaletto, Watteau, Turner and Hogarth hang in the tiny picture room on ingeniously hinged panels that fold open to reveal yet more pictures underneath, but somehow it’s not individual works of art you remember about a visit to the Soane, it’s the ensemble. With its top-lit galleries, double- height spaces and gloomy subterranean vaults, no building in London has quite the same atmosphere.

On evenings when the house is illuminated by candlelight, for example, the catacombs in the crypt become the setting for a gothic novel – one which, for all its macabre fantasy, every so often you catch mocking itself. We’ve lost two other great collections from this period – Fonthill and Strawberry Hill. The Soane Museum survives intact to give us a sense of what they must have been like.

In 1833, by a special Act of Parliament, Soane left his house at 13 Lincoln’s Inn Fields and its contents to the nation. This is not the place to explain the subsequent history of his bequest, but the museum as it is constituted today consists of the building where Soane lived and displayed his collection (No 13) and the two houses that flank it (12 and 14). These two ancillary buildings have been a godsend, enabling the director and trustees to preserve Soane’s house and collections intact while at the same time allowing the museum to expand.

For the first 100 years of its existence, the Soane was lucky enough to fall out of critical favour. Dowdy, old-fashioned and unvisited though it was, general indifference meant that it remained untouched, a time capsule awaiting rediscovery. In the 20th century a series of remarkable directors, including Sir John Summerson, Peter Thornton and Margaret Richardson, brought it back to life while staying true to Soane’s wishes that it should be kept as he had left it and opened to the public free of charge.

To this day only 70 visitors are allowed at a time, which often means a queue outside. Labels and lighting are discreet; there is no information desk, cloakroom or café. Far from discouraging visitors, the lack of amenities we take for granted in other museums only adds to the Soane’s cult status. Last year it attracted 110,000 visitors.

Recently I went to see the current director, Tim Knox, a 48-year-old architectural historian who came to the Soane six years ago from the National Trust and who, for my money, is the most interesting museum director of his generation. Knox recently launched a public appeal to raise the final £500,000 of the £7 million he needs to fund a restoration and development project that will transform and enhance a now cherished institution.

The first phase will see the interior of No 12 Lincoln’s Inn Fields transformed by the addition of a shop, cloakroom, lift, conservation studio, archive and exhibitions gallery, as well as offices for the staff. My first question is obvious: why does the museum need all these?

Knox has clearly thought about that question, and he’s ready with his answer. “This isn’t the usual museum makeover,” he says firmly, “it’s micro-surgery.” And then he’s off and running. “The Soane still has only one entrance – the front door. That means that anyone who visits will have the physical experience of entering a private house. Rather than destroy that experience by creating a cloakroom off the front hall, we’ve put the cloakroom next door in No 12. Visitors will be required to leave their coats and bags there, and then come back. A visit to the Soane starts from the moment they step through the front door.” And if it’s raining?

“We’ll provide them with umbrellas. It’s worth it to keep the house exactly as it was.” He points out that No 14 has already been adapted for use as the Study Centre, Research Library and Education Department without impinging in any way on the visitor’s experience next door.

When Knox first came to the museum, he told me, it took him a year to get a feel for what needed to be done. “I knew I had to look at all three buildings as a whole in order to preserve the integrity of the central house. The great revelation came when I realised that by moving the offices at the top of the main house to the building next door, we could put back Sir John Soane’s private apartments to what they had been. After that, we started looking for the original furniture – and though we’ll never be able to retrieve items such as Sir John’s false teeth or Mrs Soane’s knitting needles, we discovered that 90 per cent of the objects listed in the inventories are still somewhere in the building.”

The rooms he wants to reinstate are the private family apartments that were dismantled soon after Soane’s death. They include his bedroom and bathroom, his wife’s morning room, and a small chamber he called the “oratory”, which was a former dressing room he arranged as a shrine to his wife, who died less than two years after they moved in.

Not only does Knox have most of the original furniture, but he knows where it was in the house. That is because in the 1820s Soane employed architectural students to paint watercolours showing all the interiors, and after his death in 1837 inventories record the contents of each room.

When I ask him what will change about the Soane, his answer is “not much, at least outwardly”. In the age of the McArtgallery, this man has the right idea. All he wants to do, he says, is to open the Soane up, and to ensure it survives for another 200 years.